In recent years, industrial robots have been studied for use in cooperative work with humans, and a number of industrial robots capable of such cooperative work have been developed and marketed by various manufacturers. A speed reducing device is known as an important technical component for achieving an operation of such an industrial robot. The speed reducing device is combined with a servomotor so as to constitute a joint of the industrial robot. A condition required of the speed reducing device used in the industrial robot is reduced backlash.
Furthermore, in recent years, humanoid robots have been actively studied and are expected to deliver excellent performance in various fields. A speed reducing device is known as an important technical component for achieving an operation of such a humanoid robot. The speed reducing device is combined with a servomotor so as to constitute a joint of the humanoid robot. A condition required of the speed reducing device used in the humanoid robot is reduced backlash.
Examples of a speed reducing device reduced in backlash include a planetary gear speed reducer, an eccentric oscillating speed reducer, and a strain wave gearing speed reducer. The strain wave gearing speed reducer, in particular, is not only reduced in backlash but also high in speed reduction ratio, lightweight, and compact and thus has seen extensive use in joints of compact industrial robots and humanoid robots (Japanese Patent Application Publication No. 2014-84989).
The strain wave gearing speed reducer, however, is disadvantageous in the following respect. That is, the strain wave gearing speed reducer has a unique configuration in which a flex spline is bent into an elliptical shape by a wave generator, and teeth thereof are engaged at its long axis portion with inner teeth of an outer ring, and thus the strain wave gearing speed reducer has a property of readily leading to a phenomenon in which, when subjected to an external impact, the teeth of the flex spline and the internal teeth of the outer ring are disengaged from each other (loss of synchronism).
In a humanoid robot intended to walk with two legs, in addition to an impact undergone due to tipping or the like, an excessive load on a speed reducing device unexpectedly generated at the time of performing an intended operation is also exerted as an impact on the speed reducing device. When the strain wave gearing speed reducer having a flexible configuration is subjected to such an external force, loss of synchronism is readily caused, and there also occurs damage to gears therein, resulting in a failure to perform an intended operation.
In the speed reducing device used to form a joint of such a humanoid robot, it is extremely important to prevent occurrence of loss of synchronism and damage to the gears from the viewpoint of stabilizing an operation of the humanoid robot and eventually enhancing commercialization of the humanoid robot.
To this end, it has been conceived to provide the speed reducing device with an impact unit formed of an elastic member.
On the other hand, it is also desired that a load torque of the speed reducing device in operation be measured for the purpose of safe and stable use of the speed reducing device.